Water-cooling attachment for projection arc lamps



Aug. 9, 1949. H. HUFF 2,478,533

WATER'COOLING ATTACHMENT FOR PROJECTION ARC LAMPS Filed Oct. 12, 1948INVENTOR. HAROLD I. HUFF ATTORNEY Patented Aug. 9, 1949 WATER-COOLINGATTACHMENT FOR PROJECTION ARC LAMPS Harold I. Huff, Los Angeles, Calif.

Application October 12, 1948, Serial No. 54,047

Claims.

This invention relates to arc lamps for motion picture projectors andthe like, and is particularly useful in projector arc lamps of thereflector type although it is not necessarily limited to use withreflector lamps.

An object of the invention is to improve the illumination produced by aprojector arc lamp.

Another object is to reduce the rate of carbon consumption withoutreducing the light.

Another object is to control the direction of the flame or tail of theare so as to prevent injury to the reflector in a reflector type lamp.

Still other more specific objects are: to reduce flicker; to reduce ashdeposit within the lamp housing; to prevent color production andmaintain a pure white light on the screen; to eliminate need of usingmetallic coated carbons; to maintain constant resistance in the arccircuit, which keeps the current constant and maintains a uniform craterin the positive carbon; to burn the 1 follow of a particular embodimentof the inveni tion.

Broadly, the present invention consists of water cooled apparatus forcooling and conducting current to the positive carbon of a proiecticnarc lamp at a point thereon closely adjacent to and at a constantdistance from the arc. The cooling of the carbons closely adjacent thearc has the direct advantages of increasing the depth of the crater inthe positive carbon, and causing the metal of a metallic coated carbonto burn clean. It also has the advantage of permitting conduction of thecurrent to the carbon at a point thereon spaced a short, constantdistance from the arc, which results in the indirect advantages of:eliminating necessity of using metal coated carbons; maintainingconstant resistance in the arc circuit; enabling the use of heaviercurrents in carbons of given size; and facilitating the automaticfeeding of the carbons in proper relation to maintain exact focus.

The invention also permits the use of larger carbons with the samecurrent while producing the same light intensity, under which conditionsit has the advantage of greatly increasing carbon life. Thus with thepresent invention, 70 amperes of current with a 9 millimeter carbongives the same light on the screen as amperes through an 8 millimetercarbon with prior projectors, and the 9 millimeter carbon, when usedwith my attachment, will last twice as long as the 8 millimeter carbonin the conventional lamp.

The production of ash deposit on surfaces within the lamp housing isreduced, by use of the invention, to such an extent that less deposit isaccumulated in a week with the invention than in a single day withoutthe invention. The resultant cleaner reflector surface increases thelight intensity and lessens the heating of the reflector.

An important feature of the invention is the simple and ruggedconstruction of my attachment whereby it is reliable in operation andgives long service without undue maintenance expense and trouble.

In the drawing:

Fig. 1 is a side elevational view with portions broken away of areflector type projection arc lamp incorporating a water cooledattachment in accordance with the present invention;

Fig. 2 is a plan view of the attachment, the view being taken in theplane IIII of Fig. 1;

Fig. 3 is a rear elevational view of the attachment showing a portion ofthe projector in section, the view being taken in the plane III-III ofFig. 1;

Fig. 4 is a detailed vertical sectional view taken in the plane IVIV ofFig. 3;

Figs. 5 and 6 are cross sections taken in the planes VV and VI-VIrespectively of Fig. 4; and

Fig. '7 shows the relative shapes of a copper coated carbon after beingused in a lamp not equipped with the invention, a copper coated carbonafter being used with the invention, and an uncoated carbon after beingused with the invention.

Referring first to Fig. 1 there is shown a conventional lamp housing Inpositioned back of a projector H. Near the rear (left) end of thehousing I9, is a concave mirror I2 which is axially aligned with theoptical system of the projector ll. Positioned in the optical axis arethe negative carbon l3 and the positive carbon 1 4 between which the arcis formed. The carbons are longitudinally supported and fed by theconventional carriages, only the carriage It for the positive carbon I4appearing in Fig. 1. As these projectors are ordinarily used, carriageI6 not only physically supports the carbon id but also supplies thecurrent thereto.

In accordance with the present invention, a

water cooling attachment i8 is provided which engages the positivecarbon hi adjacent its tip, cools the carbon, and constitutes thecurrent connection thereto.

The carriage l6, and a corresponding carriage for the negative carbonl3, are usually motor driven to automatically feed the carbons as theyburn away, and they still perform this function when my water coolingattachment i3 is ernployed. However, since automatic mechanisms are wellknown in the art and do not constitute a part of the present invention,no feeding mechanism is described herein.

Referring to Fig 4, the water cooling attach-- ment of the inventioncomprises an annular water jacket 2E having a central passage 2i ofsomewhat larger diameter thanthe positive carbon l4, and defining awater chamber 22 through which cooling water is circulated. Thiswatermay be conducted into the chamber 22 through a; conduit 2-4:andexhausted from'the chamber through conduit 25:. For convenience, theconduits',-2A;@ and- 251. may, extendinto a header blocka,-26 to whichcopper tube-connections may be made .toganyzsuitablesource. of;supplyexhaust. Thawater'jacket-lt-is supported ina ringizz'himwhich. it:maybe looked as by a pa r of set qscrews-s289.. The ring :21 is.mountedon the uppert 'end'.otra'rrintegralj rod 25!; the latter beingldckedrbyzsetrscrews' 60 (Fig; 6) to; a member 3%] whicluin-turn has:.a;ball*sur:face thereon whichengagesrtwitl'r' a:- socket 3J5" intthexupperendof a bracket';3 2;.,the member. .39 being adapted .to bev clampediinthezsocket: in thebracket. 32b a screw 33:. .ThealiowerendoftheLbracKetSZmay be secured as -by screwsfilito the. endaof. the bed 55f the.lamp:-.-housing.z. The.:ball and. socket. connec:-.

fer' bushing 35- which: is screw threaded. into.

screw; threads; 3.! e'provi'ded for. that purpose in theiwatenjacket'mrat the. front end: of. the central passagez'litherein. Byvirtuelof' its-threaded connection to the water jacket, the bushing isirr-zverygood thermal conductive relation: thereto, and it is accuratelydimensioned astto': its bore 33' so; that itsfitsethecarbon:Mfsufliciently closely tce be. in very:- good thermal conductiverelation thereto. Because of the fact that carbon is a relatively poor'heata conductor, most of the heat generated-in the tip. portionof'thecarb'on te by theiarc istransferred-though the bushing 35 tothetwaterjacket'and' conducted away by the circulation ot watertherethrough As is well known, the usual are produced in a projectorlamp of the type. hereirr discussed, prodiices av relatively long flameor tail which if directed toward the mirror l2= may blacken. or causebreakage of the latter. I have found that iii-accordance with thepresent invention a magnetic-1 deflector for the tail of the arc can beconveniently incorporated inmy water cooling attacliment; This deviceconsists of a U-shaped element 4010f paramagnetic material such as softiron-,, the two arms ofwhich are clamped against the fi'ont. end 4|. ofthe water jacket by a shoulderAl on thebushing 35, this shoulder 42.being the rear face of an expanded head. 44 formed on the forward endof. the bushing. The enlarged feedin head 44 not only serves to anchorthe U-shaped arc deflecting member 49 but also functions to absorbradiant heat from the arc and help to limit the total rise intemperature within the lamp housing. As shown in the drawing, the bowportion 40a of the U-shaped arc deflecting member is positioned at thetop and the open ends 46b of the member are bent rearwardly. Itis' foundthat this particular configuration is most effective in some instances,but in other instances it is found best to leave the ends tiib straightand/or to orient the U-shaped member in. some. positionother than thevertical. The best position for any particular lamp can be readilydetermined by experiment.

As previously indicated, in accordance with thepresentinvention, currentis transmitted to the positive carbon I' l adjacent the tip thereofthrough the water cooling attachment instead of through the usualcarriage l5. Connection is made through. contact means consisting of'apair of. substantially semi-cylindrical brushes a? and 6'8; that,slidably grip the carbon it, the brushes being pressed against thecarbon by a helical tension spring 49 that is extended around thebrushes Electrical connection is preferably made-to each of the brushes4i and 48 by sepa-' ratepigtail connections 56- which-inaybe extended tothe water connection block. 25 which is grounded. to the frame. of themachine. The brushes t? and 43 may be of copperor a mixture of copperand graphite, the latter having a lower coefficient.- of frictionagainst a copper-coa-ted carbon, and the former having lower coefficientagainst an .uncoatedcarbon- To support the brushes 4? and as there areprovided. extending fromthe rear end or" the water jacket 23 av pair ofdiametrically disposed extensionsgSZ- and 53- which connecttoand supportat their rear end 3,. disc member 5 the latter having a central aperture55- through which. thecarbon It extends. The extensions 52. and 53together with the rear face 5? of the water jacket andthe front face 58of the disc member define a pair of approximately semicylindrical brushslotsdimensioned toslidably receive the brushes 41 and 38;.

Itis well'recognizedthat the resistance of'arc carbons is high, forwhich reason it has been customary-toprovide them with copper coatingsto conduct the current. burns; away cleanat the highly heated tipsadjacentthearc in my system. However when my water cooling attachment isnot employed the copper. coating sometimes fuses intoglobulesnear-thetips of the carbon which globules interfere with'the:production of a normal arc. The present system not-only improves theoperation with copper;.coa ted, carbons. but enables the use of;uncoated carbons, which are cheaper. is becausetne brushes d! and t8contact the carbonsrelatively close to the tips thereof and at aconstant distance from the tips. The current flows through suchv a shortlength of the carbon that thevoltage drop therein is relatively smalland the water cooling prevents materially heating of the carbons by thepower consumed in them.

Theevol-tage drop in. carbon M- remailns substantially constant at alltimes because the distancethat the current flows through the carbonremains constant. This aids greatly in maintaining the uniformity of theare.

.It is. found. that the water cooling, attache to tr bu te iall to; t e;i ma o This copper coating This a better crater in the positive carbonl4. Specifically, the crater is deeper, larger in diameter, and remainsmore constant in shape during continuous operation. A deep crater isdesirable because it reduces the size of the flame or tail rising fromthe arc. Changes in size of the crater are undesirable because theyproduce colors and flicker on the screen.

The use of the invention produces a flatter illumination on the screenthan is obtainable with the same lamp without the water cooling. Thisappears to be due to the fact that the water cooling of the positivecarbon adjacent the tip thereof increases the diameter of the luminouscrater which constitutes the light source. Thus by comparison of carbonA and B in Fig. 7,. it will be observed that the uncooled carbon A has alonger taper and smaller tip diameter than the water cooled carbon B.This is due to the fact that because carbon B is maintained at a lowertemperature, there is less external combustion rearwardly of the tip. Bythe same token, the copper coating does not burn as far back on thewater cooled carbon B as on the uncooled carbon A. Carbon C in Figure '7is typical of the tip shape of an uncoated carbon that has been usedwith the water cooler of the invention. It will be observed that itapproximates the tip shape of carbon B. Uncoated carbons can be usedwith perfect satisfaction with my water cooler, whereas it is impossibleto use them with the conventional lamp because of the heat generatedwithin the carbon itself by the passage of the current therethrough.

The water cooling attachment reduces the heat waves in the air withinthe lamp housing and thereby reduces variations in intensity of light onthe screen.

Although I am unable to explain the phenomenon, I find that with thewater cooling attachment of the invention a larger than normal carboncan be employed without increasing the current and without reducing thelight, while markedly increasing the life of the carbon.

Thus tests were run on the same projector using an 8 millimeter coatedcarbon without water cooling as against a 9 millimeter uncoated carbonwith the Water cooler of the invention. In each case, the current wasmaintained at 70 amperes. tensity on the screen measured 7-10-'7 (leftside, center, and right side respectively) whereas with the invention itmeasured 8-118. Using the smaller, copper coated carbon without theinvention, the rate of carbon consumption was 3 minutes 6 seconds perinch, as against 5 minutes 7 seconds for the larger uncoated carbon withthe invention. The disparity in carbon cost is much greater, the costper hour without the invention being 22 cents as against 12 cents withthe invention. Tests made under identical conditions (employing theinvention) with a 7 millimeter copper coated carbon and only 50 amperesgave light intensity on the screen of 8-l0 8 (better than was obtainedwith an 8 millimeter carbon and 70 amperes without the invention) a rateof carbon consumption of 6 minutes 12 seconds per inch, and a cost perhour of only 9 cents.

Although for the purpose of explaining the Without the invention, thelight ininvention, a particular embodiment thereof has been shown anddescribed, obvious modifications will occur to a person skilled in theart, and I do not desire to be limited to the exact details shown anddescribed.

I claim:

1. An attachment for a projection arc lamp having positive and negativecarbons, a frame, and means on said frame for feeding said carbonslongitudinally into arcing relation, said attachment comprising: anannular water jacket dimensioned to surround one of said carbons;contact means including a plurality of contact elements between whichsaid carbon is positioned and means slidably supporting at least one ofsaid contact elements with respect to said water jacket for lateralmovement into engagement with said carbon; spring means urging at leastone of said contact elements against said carbon for producingelectrical contact between said contact elements and said carbons; abracket attachable to the lamp frame for supporting said water jacket instationary relation to said frame and in alignment with said carbonadjacent the normal arcing position of the tip thereof; conduit meansfor conducting water to and from said water jacket; and electric leadsfor conducting current to said contact means independently of said waterjacket.

2. An attachment according to claim 1 in which said contact means ispositioned at the rear end of said water jacket remote from the carbontip; and an annular heat transfer bushing of high thermal conductivityis mounted adjacent the front end of said water jacket in thermallyconductive relation therewith and dimensioned to surround said carbon inmore closely fitting relation than the water jacket.

3. An attachment according to claim 2 in which said heat transferbushing is threaded into the front end of said water jacket.

4. An attachment according to claim 3 including a generally U-shapedarc-deflecting member of para-magnetic material held against the frontend of said water jacket by said heat transfer bushing, the arms of theU straddling an intermediate portion of the bushing and lying againstthe front end of the water jacket, and the front end of the bushingextending in front of the Water jacket and having an enlarged headdefining a shoulder for clamping the arms of the U-shaped member againstthe water jacket.

5. An attachment according to claim 1 in which said means for slidablysupporting said contact means comprises a pair of diametrically disposedrearwardly extending extensions on said water jacket, and a centrallyapertured disc member supported by said extensions and definingtherewith and the rear end of said water jacket a pair of substantiallysemi-cylindrical brush slots lying on opposite sides of said extensions;said contact means comprising a pair of substantially semi-cylindricalbrushes positioned in said brush slots; and tension spring meansencircling said brushes for retaining them in said slots and urging themagainst said carbon.

HAROLD I. HUFF.

No references cited.

